Although the current mainstream in light sources for lighting are fluorescent tubes and filament bulbs, light-emitting devices with LED as light source are becoming more widely used, since, compared to a fluorescent tube or the like, when an LED is used in a light source, in addition to power consumption being low, life span being long and safety being provided of not being hot to the touch, environmental aspects are excellent with no harmful substance such as mercury being contained.
Known as light-emitting devices using LEDs are light-emitting devices provided with a constitution in which, for instance, LEDs are disposed over a metal plate comprising silver plating performed on copper serving as a reflective plate, and the LEDs and metal plate are sealed with a phosphor-containing resin comprising a phosphor included in a resin such as silicon resin.
When a sulfur-containing phosphor is used in such a light-emitting device, since sulfur-containing phosphors react readily with water, sulfuric gas such as hydrogen sulfide, sulfur dioxide or sulfur trioxide is generated, for instance, by reaction with atmospheric moisture, or the like, and problems have been pointed out, such as, this sulfuric gas corrodes a metal member, for instance, a metal member inside an element that is provided for the purpose of raising the reflectance of the reflective plate, such as an Ag-plating film (hereafter referred to as “Ag reflective film”), decreasing the reflection performance thereof, or provoking an electrical defect such as wiring disconnection.
In addition, since sulfuric gas is present in the atmosphere at hot spring resorts or the like, even when a phosphor other than a sulfur-containing phosphor is used, the possibility has been pointed out, that, due to atmospheric sulfuric gas, a metal member inside an element, such as an Ag reflective film, becomes corroded, decreasing the reflection performance, or provoking an electrical defect such as wiring disconnection.
Upon examining the techniques proposed in prior art for solving such problems regarding light-emitting devices, for instance, with the purpose of improving moisture-resistance or the like, methods of covering this species of phosphor with a glass material or the like (Patent Document 1, Patent Document 2, Patent Document 3, Patent Document 4 and Patent Document 5), the method of covering the surface of phosphor particles by a chemical vapor phase reaction method (Patent Document 6), the method of binding particles of a metal compound (Patent Document 7), and the like, have been proposed.